Pyrithione salts are well-known salts useful in a wide variety of applications. Heavy metal salts of pyrithione, including zinc, tin, cadmium and zirconium, as well as the magnesium and aluminum salts, in the form of flat platelets suitable for use in shampoo, are disclosed in U.S. Pat. Nos. 4,345,080 and 4,323,683. For example, paints containing a pyrithione salt (e.g. zinc or sodium pyrithione) plus a copper salt (e.g. cuprous oxide or cuprous thiocyanate) are known in the art, as disclosed, for example, in U.S. Pat. No. 5,057,153. U.S. Pat. No. 5,185,033 describes a process for making a paint or paint base containing copper pyrithione or pyrithione disulfide plus cuprous oxide, wherein the paint exhibits stability against gelation during storage. U.S. Pat. No. 5,246,489 discloses a process for providing in situ generation of copper pyrithione in a paint or paint base which comprises incorporating a metal salt of pyrithione, cuprous oxide and a controlled amount of water into the paint either during or after the formation of the paint.
Copper pyrithione itself is now being considered for use in supplementing or supplementing or supplanting zinc pyrithione in view of the fact that copper pyrithione is more favored from a low-toxicity standpoint and provides stability against gellation in products such as paint during storage prior to use. However, seemingly straight-forward processes for producing copper pyrithione, such as by contacting an aqueous solution of any water soluble copper salt with an aqueous solution of sodium pyrithione, have now been found to provide a gelled precipitate of copper pyrithione. The gelled precipitate exhibits poor flowability characteristics, causing processing problems such as flowability and filterability difficulties for the gelled copper pyrithione.
New processes for producing copper pyrithione while avoiding this gellation or thickening problem during production of the copper pyrithione solution or dispersion, would be highly desired by the biocides manufacturing community. The present invention provides are such solution.